After preparing a gypsum mould of the damaged tooth, which is to be completed, the technician produces a metal cap which covers the residue of the damaged tooth. On this cap there is positioned a viscous mixture comprising porcelain powder and a predetermined shape is formed, adapted to replace the tooth. The product is then placed on the movable support of the furnace and this is gradually introduced into the interior of the vacuum furnace for drying and firing.
The interior temperature is increased in a predetermined manner, up to the required temperature which is generally of the order of about 1000.degree. C., while a reduced pressure is established, and the mixture is thus converted to the desired glazed porcelain, converting the granular mixture to a homogeneous mass. The heating conditions have to be adjusted according to the nature of the starting materials, and up-to-date furnaces are preprogrammed to carry out such heating and cooling sequences in an essentially automatic manner. The furnaces are equipped with a micro-processor, and this is provided with suitable software for the required process steps.
It is one of the drawbacks of existing furnaces that there exists only one program for the drying and firing cycle of the dental workpiece. Thus, when such item is ready, it is removed from the furnace, the next item is positioned on the support, if required, a new program is established and the workpiece is subjected to its drying and firing cycle.
Such use of the rather expensive equipment is not economical and only one technician can use the furnace at a given time.
The novel furnace of the invention provides more than one support for the dental workpieces, and also a number of program settings according to the number of supports. Thus, while one workpiece is being fired, the next one or next ones can be prepared, the corresponding drying and firing programs can be set and when the first item is finished, it is possible immediately to continue with the drying and firing of the next item.
It ought to be pointed out that the drying and firing cycle comprises a plurality of steps and parameters, such as temperature increase rate, duration of firing, vacuum at each stage, rate of decrease of temperature, etc. Actually, some firing cycles comprise up to about 10 various parameters which have to be pre-programmed.
Thus it is possible to use a furnace in a manner that one item after the other is dried and fired, using the multiple supports and programs to attain a much better economics of the entire work process.